Compound semiconductors containing phosphorus (P) as a group V element, such as InGaAlP, InGaAsP, GaP, GaAsP, and GaNP, have high P vapor pressure. Thus, they are subjected to epitaxial crystal growth under the P vapor pressure that is maintained several hundred times higher than the vapor pressure of group III elements such as In, Ga, and Al. Therefore, in vapor deposition techniques including MOCVD, part of thermally decomposed material gas is used for crystal growth of compound semiconductors, whereas much of the rest not used for crystal growth is cooled and deposited as reaction product in the growth chamber.
With the repetition of epitaxial crystal growth, the amount of deposited reaction product gradually increases, and the impurity concentration in the growth chamber is deteriorated, thereby preventing epitaxial crystal growth. For removing reaction product and recovering a suitable condition for epitaxial crystal growth, a maintenance operation is conducted. Reaction product contains a large amount of P and P compounds. If they are exposed to the atmosphere, P reacting with oxygen may catch fire and endanger the maintenance operation for removing reaction product.